Gravimetry

  Gravimetry

• Gravimetric analysis or quantitative analysis by weight is the process of isolating and weighing an element or a definite compound of the element in as pure a form as possible. 
• The element or compound is separated from a weighed portion of the substance being examined.
• A large proportion of the determinations in gravimetric analysis is concerned with the transformation of the element or radical to be determined into a pure stable compound which can be readily converted into a form suitable for weighing. 
• The weight of the element or radical may then be readily calculated from a knowledge of the formula of the compound and the relative atomic masses of the constituent elements.

    The separation of the element or of the compound containing it may be effected in a number of ways, the most important of which are: 

1. precipitation methods; 
2. volatilisation or evolution methods; 
3. electroanalytical methods; and 
4.  extraction and chromatographic method

 Only the Precipitation method is discussed in detail in this chapter.

Advantages of gravimetric analysis:

• It is accurate and precise when using modern analytical balances; 
• Possible sources of error are readily checked, since filtrates can be tested for completeness of precipitation and precipitates may be examined for the presence of impurities; 
• It has the important advantage of being an absolute method, i.e. one involving direct measurement without any form of calibration being required; 
• Determinations can be carried out with relatively inexpensive apparatus, the most expensive requirements being a muffle furnace and, in some cases, platinum crucibles.

Disadvantages of gravimetric analysis:

• The technique is tedious as it involves a number of steps. 
• It is time consuming compound to the other analytical methods.